Whether employed as a motor or as a generator, the capacity of a dynamoelectric machine can be greatly increased by liquid cooling its various components. Where the application to which the dynamoelectric machine is to be put warrants the expense of liquid cooling, little difficulty has been experienced in cooling stator components since, if for no other reason, the same are stationary. At the same time, the cooling of rotor components not only may require relatively sophisticated couplings such as transfer tubes or the like, but proper overall design as well or else operational inefficiency may come into the system.
More specifically, if proper care is not taken in designing the coolant flowpath for a rotor, the coolant may enter the air gap between the rotor and the stator and generate so-called "windage losses" which decrease the efficiency of operation of the machine. In order to avoid such windage losses, it has heretofore been necessary to expend considerable effort to provide a flowpath design that will not allow coolant to enter the air gap; and this in turn has increased the cost of rotor cooling systems.
Thus, there is a real need for an inexpensive but reliable system for achieving rotor cooling in a dynamoelectric machine without impairing operational efficiency of that machine. The present invention is directed to fulfilling that need.